1. Field of the Invention
This invention relates to an installation tool for landing a casing hanger in a wellhead and setting a seal assembly in the annulus between the casing hanger and wellhead in a single trip. The installation tool can perform these functions without requiring any rotation of the drill pipe string used for lowering the installation tool, casing hanger and seal assembly into the bore of a subsea wellhead.
The non-rotational casing hanger and seal assembly running tool of the present invention is used in oil and gas drilling operations of the type typically referred to as subsea. These type of oil and gas operations have a wellhead sitting on the ocean floor. As drilling operations proceed, various sizes of casing hangers will be lowered into the wellhead, each casing hanger having a length of casing threaded into to the lower end of the casing hanger. The lengths of casing typically will be from a few hundred feet in length for the larger size casings to several thousand feet of casing for the smaller sizes of casing. The casing hanger itself is a generally tubular member with a beveled outer shoulder sized to land on a mating inner shoulder in the wellhead or a previously installed casing hanger.
After each casing hanger and attached string of casing is landed in the wellhead a cement slurry is pumped through the casing hanger and casing. This cement slurry is forced to the bottom of the casing string where it then flows around the bottom end of the casing string and back up the annulus between the casing string and the drilled hole. After the cement has been placed, a seal assembly or packoff is lowered into the wellhead where it is urged into the annulus between the casing hanger and the inner wall or bore of the wellhead. The seal assembly often requires some mechanism to urge it into its sealed or energized position to ensure a positive seal in the annulus between the casing hanger and the inner wall or bore of the wellhead.
The seal assemblies used in this type of oil and gas drilling operations are typically either an elastomeric seal using the natural elasticity of a rubber compound to seal the annulus or a metal seal using a soft metal compound formed into a plurality of lips that are deformed or energized into contact with the bore of the wellhead and outside diameter of the casing hanger to form the aforementioned annular seal. The metal seals require substantially more force to deform and energize them into their sealing configuration. Previous designs in the industry have either used torque or annulus pressure to energize these metal seals. Those designs utilizing torque have used rotation of the drill string to operate a threaded ring to apply the needed force. These designs have a couple of major limitations: it is difficult to determine how much of the applied torque is being applied to the threaded ring and how much of the torque is being expended in rotation of the long drill pipe string and the drag of the drill pipe string on the wellbore and as wellheads are deployed in ever greater water depths more of the applied torque is lost in the drag of the drill pipe string on the wellbore than is applied to the threaded ring. The previous designs using annulus pressure have been limited by the pressure that can be applied in the annulus between the inner and outer casing strings being sealed. This pressure limitation prevents enough pressure from being generated to generate the substantial force required to energize a metal seal.
Additionally, it is preferable if the tool used to lower the casing hanger and set the seal assembly in the casing hanger—wellhead annulus can accomplish these tasks in one trip. As wells are drilled in ever deeper water depths, the time for lowering a tool to the sea floor and retrieving it increases dramatically and this translates into higher drilling costs as the cost of the rig time required to perform these operations is high. It is therefore desirable to have an installation tool that can lower a casing hanger and associated seal assembly into a well bore, land the casing hanger, allow cementing and energize the seal assembly in a single trip without requiring rotation of the drill string. The non-rotational casing hanger and seal assembly running tool of the present invention offers a substantial improvement by offering a tool that can perform these functions in a single trip and allow testing of the installed seal assembly without requiring rotation of the drill striing.
2. Description of Related Art
U.S. Pat. No. 4,903,776 to P. C. Nobileau et al. shows a casing hanger running tool using drill string tension to set the packoff. The axial movement of the drill string is used in conjunction with differential area pistons to apply force on a sleeve to set the packoff.
A casing hanger running tool using string weight is disclosed in U. S. Pat. No. 4,928,769 to L. J. Milberger et al. This device also uses the weight of the drill string acting on differential area pistons to drive a setting sleeve downward to set the packoff.